1. Field of the Invention
The present invention relates to a continuous gas analyzer for continuously analyzing a target gas component contained in a sample gas, and more particularly, it relates to an analyzer such as an SO.sub.2 measuring device for analyzing a component which is exposed to interference by moisture.
2. Description of the Background Art
FIG. 1 shows a conventional SO.sub.2 measuring device. A sample gas introduction passage 6 for sucking a sample gas by a suction pump 2 and introducing the same into an analyzer 4 is provided with a flow control valve 8 on a position upstream the pump 2, while a dehumidifier 10 is provided between the pump 2 and the analyzer 4 as a constant humidity device for keeping the moisture concentration in the sample gas at a constant level. A standard gas introduction passage 14 is connected to the passage between the pump 2 and the dehumidifier 10 through a three-way cock 12. The standard gas introduction passage 14 is connected with cylinders 16 and 18 of a zero gas containing no SO.sub.2 and a span gas containing SO.sub.2 in a constant concentration through switching valves 20 and 22 respectively. The three-way cock 12 is switched and the switching valves 20 and 22 are opened/closed for switching and introducing the sample, zero and span gases into the analyzer 4 through the dehumidifier 10.
The analyzer 4 comprises a data processing part having a calibration curve storage part for holding measured values of the zero and span gases supplied from the standard gas introduction passage 14 as calibration curve data for calculating the sample gas concentration on the basis of the calibration curve data.
In relation to measurement of SO.sub.2, a detection part of the analyzer 4 also has sensitivity to moisture. Therefore, moisture positively acts on detected values as moisture interference.
In calibration, the three-way cock 12 and the switching valves 20 and 22 are switched to introduce the zero and span gases into the analyzer. At this time, the standard gases are also supplied with moisture of a constant concentration from the dehumidifier 10. Thus, moisture interference constantly acts between zero and a span value.
FIG. 2 shows the relation between calibration curves and moisture interference. When the zero and span gases are guided to the analyzer 4 through the dehumidifier 10, a calibration curve (b) is formed due to positively oriented indication by moisture interference. Due to calibration in a wet state containing moisture at zero and span points, however, an apparent calibration curve (a) passes through the origin after the calibration. Namely, it comes to that the calibration is made with addition of the moisture interference.
When the target gas component is SO.sub.2 which is exposed to moisture interference, the speed of response of the sample gas is retarded due to adsorption of the target gas component by the moisture in a wet state, and hence the calibration time is increased. Consequently, the zero and span gases are consumed in large amounts and the capacities of the standard gas cylinders cannot be reduced, to hinder miniaturization of the overall device.